He is Haru's cousin. Mitsuyoshi acts as a father figure for Haru, looking affectionately after him. Haru calls him "Mi-chan". Mitsuyoshi often goes on trips with Haru and his friends, later earning the attention of Asako Natsume.

Asako eventually confesses to Mitsuyoshi, but he rejects her due to their difference in age. Despite this, he continues to have a friendly relationship with Asako, admitting that the shop is somewhat "lonesome" when she doesn't visit.